Foam for optical fiber cable, composition, and method of manufacturing

ABSTRACT

Embodiments of the disclosure relate to an optical fiber cable having at least one optical fiber, a cable jacket and a foam layer. The cable jacket includes an inner surface and an outer surface in which the outer surface is an outermost surface of the optical fiber cable. The inner surface is disposed around the at least one optical fiber. The foam layer is disposed between the at least one optical fiber and the cable jacket. The foam layer is made of an extruded product of at least one thermoplastic elastomer (TPE), a chemical foaming agent, and a crosslinking agent. The foam layer has a closed-cell morphology having pores with an average effective circle diameter of less than 100 µm. Further, the foam layer has a compression modulus of less than 1 MPa when measured at 50% strain.

CROSS-REFERENCED TO RELATED APPLICATIONS

This application is a Continuation application of U.S. Pat. ApplicationNo. 17/729,359 filed Apr. 26, 2022, which is a Divisional of U.S. Pat.Application No. 16/918,466 filed Jul. 1, 2020, now U.S. Pat. 11,327,260,which claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application Serial No. 62/869,929 filed on Jul. 2, 2019, thecontent of which is relied upon and incorporated herein by reference inits entirety.

BACKGROUND

The present invention is related to an optical fiber cable having a foamlayer disposed between a ribbon stack and a cable jacket and, inparticular, to polymer blend and method of forming the foam layer.Optical fiber cables incorporate a variety of materials withfunction-specific properties in multiple layers to achieve desiredperformance. For examples, the cable jacket and buffer tubes are oftenmade of polyolefin materials. The optical fiber cable may also include ametal armor layer and one or more glass-reinforced plastic strengthmembers. Though the polyolefins often provide good flexibility, thearmor layer and/or strength members may create signal attenuation whenthe cable is bent, coiled, crushed, or twisted.

SUMMARY

In one aspect, embodiments of the present disclosure relate to anoptical fiber cable having at least one optical fiber, a cable jacketand a foam layer. The cable jacket includes an inner surface and anouter surface in which the outer surface is an outermost surface of theoptical fiber cable. The inner surface is disposed around the at leastone optical fiber. The foam layer is disposed between the at least oneoptical fiber and the cable jacket. The foam layer is made of anextruded product of at least one thermoplastic elastomer (TPE), achemical foaming agent, and a crosslinking agent. The foam layer has aclosed-cell morphology having pores with an average effective circlediameter of less than 100 µm. Further, the foam layer has a compressionmodulus of less than 1 MPa when measured at 50% strain.

In another aspect, embodiments of the present disclosure relate to amethod of preparing an optical fiber cable. In the method, athermoplastic elastomer (TPE) blend is prepared that includes 100 partsof a polymer component, 0.1 to 3 parts of a chemical foaming agent, and0.1 to 2 parts of a crosslinking agent. The TPE has a tensile modulus ofat most 10 MPa at 100% secant. In the method, the TPE blend is extrudedaround an optical fiber cable core in a manner that produces a foamlayer surrounding the optical fiber cable core along a longitudinal axisof the optical fiber cable core.

In yet another aspect, embodiments of the present disclosure relate to athermoplastic elastomer (TPE) foam. The TPE foam includes an extrudedproduct of 100 parts by weight of a polymer component including at leastone TPE, 0.1 to 3 parts by weight of a chemical foaming agent, and 0.1to 2 parts by weight of a crosslinking agent. The TPE foam has aclosed-cell morphology having pores with an average effective circlediameter of less than 100 µm. The TPE foam has a compression modulus ofless than 1 MPa at 50% strain, and the TPE foam has a compression set ofno more than 5% as measured after compression to a strain of 60% for tenhours and after four hours of recovery time.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is longitudinal, cross-sectional view of an optical fiber cablehaving a foam layer, according to an exemplary embodiment;

FIG. 2 is a perspective view of a portion of an optical fiber cablehaving a foam layer, according to an exemplary embodiment;

FIG. 3 is longitudinal, cross-sectional view of a portion of an opticalfiber cable having a foam layer, according to an exemplary embodiment.

FIG. 4 is a micrograph of a TPE foam, according to an exemplaryembodiment;

FIG. 5 depicts a histogram of pore size distribution of the TPE foam ofFIG. 4 ;

FIG. 6 is a hysteresis graph of compressive stress and strain on a TPEfoam according to an embodiment of the present invention and aphysically foamed polymer blend according to a comparative example; and

FIG. 7 depicts a graph of stress and strain over time for calculatingcompression set, according to an exemplary embodiment.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION

Referring generally to the figures, embodiments of the presentdisclosure relate to a thermoplastic foam that can be extruded aroundone or more ribbon stacks and/or buffer tubes of an optical fiber cable.The foam is formed from the extruded product of a blend of thermoplasticelastomer (TPE), a chemical foaming agent, and a crosslinking agent. Byusing a chemical foaming process, the chemical foaming agentadvantageously can be compounded with the TPE and extruded within oraround a cable core without the need for any special processingequipment. That is, because the foaming action takes place chemically,no equipment modifications are necessary to physically create the foam.Further, as compared to physical foams, the foams prepared according toembodiments of the present disclosure have similar density reductions(e.g., at least 65%) with better compression set performance, at leastin part because the chemical foaming agent produces smaller pores thanphysical foaming agents. In an optical fiber cable, the foam providescushioning for the optical fibers within the buffer tube(s). That is,the foam helps prevent attenuation of the optical fibers when the cableis bent, crushed, twisted, flexed, etc. In particular, the foam, whichhas a low modulus, diminishes the transmission of outside stress forcesto the ribbon stack, which could otherwise cause fiber attenuation.

Further, in armored cable designs, the foam prevents attenuation issuescaused by armor contact during cable bending, flexing, or coiling.Additionally, the foam allows for the reduction of the wall thickness ofthe buffer tubes and of the cable jacket so as to allow for increasedfiber density within a given cable outside diameter. In this way, thefoam also allows for significantly improved cable designs along withcost reduction through elimination of free space in the tubes, reductionof cable outer diameter, and use of smaller strength members (such asglass-reinforced plastic rods). As will be discussed more fully below,the TPE foam is extruded around a central buffer tube, a ribbon stack,or stranded buffer tubes in a manner that causes it to foam. These andother advantages and aspects of the foam will be discussed in relationto the embodiments disclosed and depicted herein, especially as theyrelate to an optical fiber cable. However, these embodiments areexemplary in nature, not limiting.

FIG. 1 depicts a longitudinal, cross-sectional view of an optical fibercable 10. The optical fiber cable 10 includes at least one buffer tube12, shown as a central tube. The buffer tube 12 has an inner surface 14and an outer surface 16 that define an average buffer tube thickness T₁.In embodiments, the thickness T₁ of the buffer tube 12 is from 0.25 mmto 0.30 mm. The inner surface 14 defines a central bore 18 that extendsalong the longitudinal axis of the optical fiber cable 10 for at least aportion of the length of the optical fiber cable 10. Disposed within thecentral bore 18 of the buffer tube 12 is a stack 20 of optical fiberribbons 22. The optical fiber ribbons 22 include a plurality of opticalfibers 24 arranged in substantially planar arrays. In embodiments, theoptical fibers 24 may be held in the array via a binding matrix and atleast one coating of a curable resin.

Surrounding the buffer tube 12 along the longitudinal axis is a foamlayer 26. As used herein, each element inside the foam layer 26 will becollectively referred to as an “optical fiber cable core” 27. Thus, inthe embodiment of FIG. 1 , the optical fiber cable core 27 includes thestack 20 of optical fiber ribbons 22 and the buffer tube 12. Inembodiments, the foam layer 26 is extruded and drawn over the outersurface 16 of the buffer tube 12. Further, in embodiments, the foamlayer 26 has a thickness T₂ of from 0.5 mm to 3 mm. In otherembodiments, the foam layer 26 has an average thickness T₂ of from 0.5mm to 2 mm, and in still other embodiments, the foam layer 26 has athickness T₂ of from 1 mm to 2 mm.

Optionally, in embodiments, the optical fiber cable 10 includes an armorlayer 28 disposed around the foam layer 26. In embodiments, the armorlayer 28 is formed from a metal tape that is wrapped around the cablecore 27. In certain embodiments, the armor layer 28 is corrugated. Acable jacket 30 surrounds the armor layer 28 (if provided) or the foamlayer 26 (if no armor layer 28 is provided). The cable jacket 30 has aninner surface 32 and an outer surface 34 that define an average jacketthickness T₃. In embodiments, the cable jacket 30 has a thickness T₃ offrom 1.25 mm to 1.75 mm. In embodiments, the cable jacket 30 has athickness T₃ of about 1.50 mm. In embodiments, the outer surface 34 ofthe cable jacket 30 defines the outermost surface of the optical fibercable 10. As depicted in FIG. 1 , the optical fiber cable 10 may includestrength elements 36 embedded in the cable jacket 30 between the innersurface 32 and the outer surface 34. Exemplary strength elements 36include glass-reinforced plastic (GRP) rods and metal wire. Inembodiments, the thickness T₃ is limited on the low end of the thicknessT₃ range by the size of the strength elements 36.

In another embodiment shown in FIG. 2 , the optical fiber cable 10′includes a plurality of buffer tubes 12 stranded around a centralstrength member 38 having a coating 40. The buffer tubes 12 contain aplurality of optical fibers 24 in a loose tube configuration. The buffertubes 12 are stranded around the coated central strength member 38,e.g., in a helical or SZ-stranded manner. Thus, in this embodiment ofthe optical fiber cable 10′, the cable core 27 includes the plurality ofbuffer tubes 12, the optical fibers 24, the central strength member 38,and the coating 40. Surrounding the cable core 27 is the foam layer 26,and disposed around the foam layer 26 is the cable jacket 30.

In a further embodiment of an optical fiber cable 10″ depicted in FIG. 3, the foam layer 26 surrounds the ribbon stack 20. In the embodimentdepicted, the buffer tube 12 is excluded (in which case the cable core27 of the embodiment depicted includes just the ribbon stack 20).However, in other embodiments, a buffer tube 12 may surround the foamlayer 26, and another foam layer 26 could surround the buffer tube 12(in which case the cable core 27 includes the ribbon stack 20, the firstfoam layer 26, and the buffer tube 12). In the embodiment depicted, thefoam layer 26 is surrounded by an optional armor layer 28, which issurrounded by the cable jacket 30. Thus, in the embodiment of FIG. 3 ,the foam layer 26 is in contact with the outer surface of the ribbonstack 24 and with the inner surface of the armor layer 28. However, inother embodiments, the foam layer 26 can be in contact with the outersurface of the ribbon stack 24 and with the inner surface 14 of a buffertube 12 or with the inner surface 32 of the cable jacket 30.

Having described three embodiments of the optical fiber cables 10, 10′,10″ in which the foam layer 26 may be incorporated, the foam layer 26will now be described in greater detail. As mentioned above, the foamlayer 26 is a TPE foam formed through a chemical foaming process.

In embodiments, the foam layer 26 primarily comprises a polymercomponent, a chemical foaming agent, and a crosslinking agent. Inembodiments, the foam layer 26 comprises 0.1 to 3 parts of activechemical foaming agent and 0.1 to 2 parts of the active crosslinkingagent per 100 parts of the polymer component.

In embodiments, the polymer component is primarily comprised of one ormore TPE. In embodiments, the polymer component comprises at least 90%by weight of the one or more TPE. In embodiments, the polymer componentmay also comprise up to 10% by weight of low density polyethylene(LDPE).

A variety of TPE are suitable for use in the polymer component of thefoam layer 26. In embodiments, the TPE comprises at least one of apolyolefin elastomer (POE), a thermoplastic polyolefin (TPO), or athermoplastic vulcanizate (TPV). In an exemplary embodiment, the TPE isselected to have an unfoamed tensile modulus of at most 10 MPa at 100%secant according to ASTM D638. In other embodiments, the TPE is selectedto have an unfoamed tensile modulus of at most 5 MPa at 100% secantaccording ASTM D638.

In exemplary embodiments, suitable POE for the foam layer 26 includecopolymers of ethylene and octene or butene, such as an ethylene-octenecopolymer or an ethylene-butene copolymer. Such copolymers offer a lowmodulus at low temperature and high recovery from mechanicaldeformations. Two commercially available ethylene-octene copolymersinclude the Engage™ copolymer family and Infuse™ Olefin Block Copolymers(OBCs). Commercially available examples of TPOs include Catalloy TPOs ofSoftell grades (LyondellBasell Industries, Houston, TX), andcommercially available examples of TPVs include Santoprene™ (Exxon MobilCorporation, Irving, TX), and Sarlink® 8145 (Teknor Apex, Pawtucket,RI).

In embodiments, the chemical foaming agent comprises at least one ofazodicarbonamide, azodiisobutyronitrile, benzenesulfohydrazide, 4,4-oxybenzenesulfonyl semicarbazide, para-toluene sulfonyl semicarbazide,barium azodicarboxylate, N, N′-dimethyl-N, N′-dinitrosoterephthalamide,trihydrazino triazine, or sodium bicarbonate. In embodiments, thechemical foaming agent is introduced to the foam layer 26 via amasterbatch, which provides for ease of handling. Commercially availableexamples of chemical foaming agents include Foamazol™ (BergenInternational, LLC, East Rutherford, NJ), Hydrocerol® (Clariant,Muttenz, Switzerland), Safoam® (Reedy Chemical Foam & SpecialtyAdditives, Charlotte, NC), or similar chemical foaming agents.

In embodiments, the crosslinking agent comprises a peroxide. Inparticular embodiments, the peroxide comprises at least one of dicumylperoxide, di-tert-butyl peroxide, ditertiary amyl peroxide, tert-butylperoxide, tert-butyl cumyl peroxide, dibenzoyl peroxide, or tert-butylhydroperoxide. Masterbatch of crosslinking agent is also preferred forthe ease of handling. Commercially available examples include Luperox®(Arkema S.A., Colombes, France) and PCL (Polyvel Inc., Hammonton, NJ).The crosslinking agent is used to produce free radicals during meltextrusion and induce partial crosslinks in the TPE. The partiallycrosslinked TPE has an increased melt strength so that the foam cellcoalescence is minimized during foaming and density reduction isincreased.

In embodiments, the foam layer 26 is formed by extruding the TPE blendaround the cable core 27. Advantageously, the TPE blend can be preparedby simply mixing the polymer component, the chemical foaming agent, andthe crosslinking agent in an extruder. In particular embodiments, thepolymer component, the chemical foaming agent, and the crosslinkingagent are dry-mixed prior to adding them into the extruder hopper. Otheradditives may also be added to the TPE blend in the extruder, includingnucleating agents, processing aids, UV stabilizers, and/or antioxidants,among others. Successful extrusion of the TPE blend as a foam isachieved by adjusting the temperature and pressure profiles within theextruder to efficiently use the chemical foaming agent. Duringextrusion, the temperature at the feed zone is kept low enough toprevent premature decomposition of chemical foaming agents in the barrelwhile still allowing a melt seal to form (otherwise gas loss may occurback through the hopper). The melt zone temperature should then increaserapidly to above the decomposition temperature of the chemical foamingagent(s) and at the same time initiate the peroxide decomposition.Sufficient pressure is maintained on the melt to prevent foaming in theextruder. In embodiments, the pressure is maintained by use of a highcompression screw or temperature reduction after the melting zone of theextruder. The pressure is maintained until the TPE blend exits the dieat which point the rapid pressure drop initiates nucleation and foamingof the TPE blend. The TPE blend melt temperature at this point is keptas low as possible so that cooling can take place quickly to controlexpansion and limit escape of the gas. In embodiments, the temperatureis kept lower than that for unfoamed plastics to enhance surfaceappearance.

In the TPE blend, the TPE provides the elastomeric property to the foamwhile the crosslinking agent provides a high expansion ratio as a resultof high melt strength that results from the crosslinking. During foamextrusion, if the melt strength of the blend is too low, the bubbleswill rupture and coalesce before the foam is cooled and a poor qualityfoam with large bubbles will result. Additionally, the blend may includeone or more additives that prevent bubbles from coalescing and thatimprove stability, such as glycerol monostearate (GMS).

FIG. 4 provides a picture of the TPE foam. Using the picture of thefoam, an analysis of the pore size distribution was performed using theequivalent circle diameter (ECD) methodology, which involves tracingpore outlines within a given area and measuring the diameter of thetracings. FIG. 5 provides a histogram of the pore size distribution. Ascan be seen in FIG. 5 , the pores have an ECD of 100 µm or less. Inparticular, the pores have an ECD of 50 µm or less. In particular, thepores have an ECD distribution with a peak between 20 µm and 30 µm. Inembodiments, the TPE foam has a density reduction (as compared to anunfoamed blend) of at least 60%, more particularly at least 65%.

The TPE foam specimen of FIG. 4 was tested to determine the compressionmodulus at 50% strain using a parallel plate compression fixture on anelectromechanical tensile test machine (MTS Insight 5 kN) according toASTM 3574 - Standard Test Methods for Flexible Cellular Materials. Inparticular, the TPE foam specimen was loaded at a constant strain rateof 30% per min until 50% strain was reached. Thereafter, the specimenwas unloaded at a constant rate of 30% per minute until the parallelplates returned to their original position. FIG. 6 shows themodulus-strain curve, for the TPE foam. As can be seen in FIG. 6 , theTPE foam had a compression modulus of less than 1 MPa at 50% strain. Inparticular, the TPE foam has a compression modulus of less than 0.25 MPaat 50% strain. Further, the TPE foam returned to a strain of less than0.1 (e.g., about 0.05) when unloaded.

The foam of FIG. 4 was also subjected to compression set testing.Compression set measurement was assessed via a parallel platecompression fixture on a dynamic mechanical analyzer (DMA Q800,available from TA Instruments, New Castle, DE). During testing, the TPEfoam specimen was compressed at a constant strain of 60% for 10 hours.The compression load was removed from the foam specimen, and thespecimen was monitored for strain relaxation over the next 4 hours. Theresults of the compression test is shown in FIG. 7 . As can be seen inFIG. 7 , the specimen only experienced a compression set of less than5%. That is, after compression at a strain of 60% for 10 hours, thespecimen recovered to 95% of its original thickness after strain wasremoved.

Foams having different compression modulus can be utilized in the sameoptical fiber cable 10, 10′, 10″. For example, the optical fiber cable10, 10′, 10″ may consist of one or more layers of foams. In oneembodiment, the optical fiber cable 10, 10′, 10″ includes a relativelysofter inner layer (i.e., lower modulus), which directly contacts thestranded core or central tube, and a relatively stiffer outer layer,which may contact with cable sheath or armor layer. Such a foamstructure allows for further improvement of the cable mechanicalperformance by absorbing the strain/stress transferred to the core.Specifically, a softer inner layer reduces the compression stressimposed on a stack of optical fiber ribbons during bending and cablecoiling. A stiffer outer layer together with the softer inner layer candeform under crushing and impact loading and therefore functions asspacer to reduce the loads. In embodiments, increasing the amount ofchemical foaming agent or decreasing the amount of crosslinking agentreduces the compression modulus (e.g., to create the lower modulus innerlayer), and decreasing the amount of chemical foaming agent orincreasing the amount of crosslinking agent increases the compressionmodulus (e.g., to create the higher modulus outer layer).

The embodiments of the optical fiber cables 10, 10′, 10″ disclosedherein are envisioned to pass relevant telecommunications standards forreliability. For example, the malleability and flexibility of the foamallows movement of the ribbon stack subunit during cable coiling at 15xthe cable outer diameter (i.e., minimum bend radius) over thetemperature range of -30° C. to 70° C. and allows stress dispersionduring impact, crush, and other mechanical tests. Further, by replacingfree space in the optical fiber cables 10, 10′, 10″ with foam, theattenuation issue experienced by some conventional cables during thecable crush testing at the corner fibers of the ribbon stack isaddressed and attenuation remains below 0.15 dB at all the corner fibersduring the 110 N/cm compression load of Telcordia GR-20. Additionally,cable designs incorporating the foam layer have improved mid-spancoiling over traditional designs because the foam layer allows for muchmore robust cable twist performance without attenuation increase.Indeed, according to industry standard GR-20 for twist requirements, atwo meter piece of cable must be able to be twisted 180 degree in bothdirections without having any attenuation greater than 0.15 dB.Embodiments of the disclosed foam allow superior performance in twisttesting with three full twists (1080°) in both directions withattenuation less than 0.15 dB.

Additionally, the foam stays flexible at low temperature. The foam has abrittleness temperature below -50° C. Further, the foam is dimensionallystable over the temperature range of -40° C. to 85° C., and has ashrinkback less than 5%, as required per GR-20 industry standard forjacket components.

The combination of a crosslinking agent with a chemical foaming agentexhibits higher density reduction (>60%) than standard foams made withchemical foaming agents only. The closed cell morphology and theselection of a TPE blend deliver a balance for the TPE foam propertiesthat combines low modulus to provide stress dispersion (and subsequentfiber strain reduction) with >90% thickness recovery after beingcompressed to 60% of its original thickness. The TPE foam also deliversinstantaneous high recovery from large deformations of 50% strain.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical fiber cable comprising: a cable jackethaving an inner surface and an outer surface, wherein the inner surfacedefines a central bore that extends along a longitudinal axis of theoptical fiber cable and the outer surface is an outermost surface of theoptical fiber cable; at least one optical fiber; and a foam layerextruded to extend through the central bore that is disposed between theat least one optical fiber and the inner surface of the cable jacket,wherein the foam layer comprises: a thermoplastic elastomer (TPE) foamcomprising both a polymer component having at least one TPE and achemical foaming agent; wherein the TPE foam has a compression set of nomore than 5% as measured after compression to a strain of 60% for tenhours and after four hours of recovery time using a parallel platecompression fixture on a dynamic mechanical analyzer.
 2. The opticalfiber cable of claim 1, wherein the chemical foaming agent comprises atleast one of azodicarbonamide, azodiisobutyronitrile,benzenesulfohydrazide, 4, 4-oxybenzenesulfonyl semicarbazide,para-toluene sulfonyl semicarbazide, barium azodicarboxylate, N,N′-dimethyl-N, N′-dinitrosoterephthalamide, trihydrazino triazine, orsodium bicarbonate.
 3. The optical fiber cable of claim 1, wherein theTPE comprises at least one of a polyolefin elastomer, a thermoplasticpolyolefin, or a thermoplastic vulcanizate.
 4. The optical fiber cableof claim 1, wherein the TPE has an unfoamed tensile modulus of at most10 MPa at 100% secant as measured according ASTM D638.
 5. The opticalfiber cable of claim 1, wherein a two meter piece of the optical fibercable is capable of being twisted 1080° clockwise or counterclockwisealong the longitudinal axis without having attenuation of greater than0.15 dB.
 6. The optical fiber cable of claim 1, wherein the TPEcomprises at least one of a polyolefin elastomer (POE), a thermoplasticpolyolefin (TPO), or a thermoplastic vulcanizate (TPV).
 7. The opticalfiber cable of claim 6, comprising the POE, wherein the POE comprises acopolymer of ethylene and octene or butene.
 8. The optical fiber cableof claim 1, further comprising: at least one buffer tube, wherein theTPE foam is extruded around the at least one buffer tube.
 9. The opticalfiber cable of claim 1, wherein the at least one buffer tube includesmultiple buffer tubes in a stranded configuration in the central boreand the TPE foam is extruded around the stranded buffer tubes.
 10. Theoptical fiber cable of claim 1, wherein the at least one optical fiberincludes a plurality of optical fibers arranged in a substantiallyplanar array to form an optical fiber ribbon.
 11. The optical fibercable of claim 10, further comprising multiple optical fiber ribbonsformed into a ribbon stack, and wherein the TPE foam is extruded aroundthe ribbon stack.
 12. The optical fiber cable of claim 1, wherein theTPE foam has a brittleness temperature below -50° C.
 13. The opticalfiber cable of claim 1, wherein the TPE foam is dimensionally stableover the temperature range of -40° C. to 85° C. and has a shrinkback ofless than 5%.